The present invention relates to a paging system in a mobile communication system for service of mobile stations which include both vehicle equipment and portable equipment, in particular, relates to such a system which reduces power consumption of portable equipment.
In a mobile communication system, power consumption of a mobile station must be as small as possible so that a battery in a mobile station operates as long as possible in every charge operation. It should be noted that a mobile station consumes some power even in the waiting state (i.e. standby mode).
Conventionally, an intermittent receiver system has been used in a pocket bell system for reducing power consumption as shown in JP patent laid open publication 60-52133 dated Mar. 26, 1985, and in JP patent laid open publication 63-227134 dated Sep. 21, 1988. In that system, mobile stations are classified into a plurality of groups so that each group includes a plurality of mobile stations. Paging information is broadcast in a time slot which is specific to the related group, and the mobile stations in the group receives the time slot signal. Since the power consumption when the station does not receive the time slot is very small, the power is essentially supplied intermittently, and the charged time or the life time of a battery is long. In that system, a buffer memory is provided to store paging calls in each time slot, and the content of the memory is broadcast in the related time slot. A call originated when a related area of the buffer memory is full, is handled as a call loss.
However, a conventional intermittent receiver system has the disadvantage that the call loss largely depends upon the call occurrence, and the call loss is large when compared with that in which no group classification is used.
If we intend to provide the same call loss as that with no group classification, the number of paging slots must be increased, but the increase of the paging slots decreases the efficiency of the paging slots or the paging channels.
Another disadvantage of conventional intermittent receiver system is that both portable equipment which is carried by a person, and vehicle equipment which is carried by a vehicle, are classified into groups, while the latter equipment which is carried by a vehicle has no serious necessity for power saving, or related problems.